Hi, my first post on this forum and looking for urgent help/advice.
I live in Sydney, Australia so we have just gone into summer.
My new house of 12 months came with an established 20,000L pond with about 35-40 large koi 30-60cm plus some goldfish. My guess is most fish 15+ years old.
The pond filter is a gravity filter of approx 2000L. Its a very simple design where water circulates through a number of Japanese mats. Given the age and size of the fish, its must have worked well historically. There was no aeration in the pond other than as water return from the filter into the pond. I think the pump is 20,000L per hour based on the model number.
Thankfully no major issues or fish loss since I moved in until November. However, since then I lost 15 large koi to mid Dec. I would find the koi in the morning on their back, sometimes still breathing fighting for life, but unable to maintain bouyancy. Goldfish were resilient but a few seemed to pinecone over the same period.
In general koi behaviour became very unusual - very lethargic, flashing, red streaks, stayed at bottom of deep end of pond, some had locked fins, very low appetite.
I have closely monitored water quality / done frequent 25-40% water changes and put in more aeration but still no improvement.
My self diagnosis was bacteria or parasite. I salted the pool to 0.6% for 1 week. Fish became slightly more active. No deaths for a week and then I lost another couple.
I chanced across a Fish Vet who made a house call. She scraped a few goldfish didn't find anything (we couldn't net any of the koi). She suspected parasite from the pale gills but thought the salt level may have been a factor for not finding anything. She told me to reduce the salt level and she would do a second visit.
Over next 2 weeks reduced salt to 0.05%. The vet returned after I lost a other couple more koi. We did a scrape of some of the goldfish and she found flukes.
She prescribed 200g of praziquantel powder for my 20,000L pond. She said with this type of fluke one treatment would be sufficient. She also said we should inject anti-biotics into the fish to address any secondary bacterial infection. Given the number of fish and difficulty in netting them, she gave me some powder antibiotic to coat the fish food instead. She also asked me to increase the salinity to up to 0.3%.
Its been 48 hours and the fish behaviour remains strange post the praziquantel dosing.
All the koi have now moved from the deep end of the pond to the shallow end, and appear to be floating close to the surface. I don’t see them gasping for air but they are very lethargic and zero appetite. A positive is flashing is seldom which suggests to me the praziquantel may have been effective in addressing the flukes.
Given the zero appetite, I have not been able to start the antibiotic treatment through the food. This coupled with the behaviour of the fish continues to make me very concerned.
Appreciate any feedback from others on whether this behaviour is expected and their appetite will return or I should be taking other measures to save the fish.
FYI, my current water quality readings are below based on API test kit. I don’t have a KH test. Thanks in advance.
Ph 6.5
Ammonia 0-.25ppm
Nitrite 0-0.25ppm
Nitrate 0-5.0 ppm
Salinity 0.3% (digital meter)
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Originally Posted by SimonW
Zone 7 A/B
